It is proposed to continue and expand research on the in vitro biosynthesis of homarine and pyridine carboxylic acid in minces and homogenates of marine shrimp. Radioactive glycine is incorporated into homarine but not by way of picolonic or quinolinic acids. Similarly, 14C-labeled sarcosine yields radioactive homarine. It is hoped to elaborate further details of this metabolic pathway. 14C-acetate is readily incorporated into quinolinic acid and N-methyl quinolinic acid but not appreciably into homarine as reported earlier. Labeled quinolinic acid is now found to be rapidly converted to its N-methyl derivative and not into homarine. Further studies will be required to determine how acetate is metabolically converted to quinolinic acid.